This invention relates to closures for containers, and particularly to caps which seal a pouring channel and after opening are retained connected to the container.
In the packaging of pressurized contents a need exists to provide a cap which in the first instance is tight with respect to gases which are wholly or partially dissolved in the contents, in particular carbon dioxide. The cap should, secondly be mechanically so stable that it is retained without substantial deformation in the opening of the container. Thirdly, the cap should be relatively easy to open, and lastly be inexpensive to manufacture and easy to apply to the container.
The use has been known for a long time of screw caps, stopperlike caps of the cork type, and tear-off metal caps, in connection with bottles and other containers intended for pressurized contents. In particular for non-returnable containers of plastics it has been found, however, that the available known cap constructions are not satisfactory, largely because of the elasticity of the plastic material. Thus it is difficult simply to use a stopper construction, the simplest variety of which is an ordinary bottle-cork, since contrary to a metal container or a glass container the mouth of a plastic container under the effect of pressure tends to yield elastically, so that a stopperlike cap is easily pushed out by the internal pressure prevailing in the container. The same is the case with tear-off metal caps of the known type, since the fitting of such caps requires a certain backing from the container mouth, and this backing as a rule is not present to a sufficient extent on thin-walled plastic containers. So-called screw caps have been used for the closing of plastic containers intended for pressurized contents, but such closures are relatively expensive, since the moulding of threads on the opening part of the plastic container is burdensome to perform and in any case diminishes the capacity in the manufacture of the containers. To solve this technical problem it has been suggested previously to use an injection moulded plastic cap of the same type in principle as that of the present application, this cap being adapted so as to be used in containers whose opening part has an inwardly directed, flexible, annular lip of plastic material. Such a cap in principle consists of two parts which, however, are joined before the cap is opened along a thin, readily breakable, annular portion. To allow the said portion to be easily breakable, it is necessary that the wall thickness within the portion in question should be small, and this in turn means that the gas permeablility will be great, especially if the material itself is not particularly gastight (e.g. polyethylene). To solve this problem while retaining at the same time the advantages of the known cap, it has been proposed in accordance with the present invention to provide a cap which is characterized in that the lower, preferably plane part of the stopperlike part is provided with an annular portion projecting from the stopperlike part, whose free edge is mainly located in the same plane as the lower edge zone of the outer part. The lower edge zone of the outer part as well as the said free edge of the annular portion of the stopperlike part are jointly covered by and fixed to a circular metal foil disc.
In a preferred embodiment of the present invention the lower part of the outer tubular body is provided with an annular recess, whose diameter coincides with or slightly exceeds the diameter of the circular aluminium foil disc. The disc is adapted so that it is accomodated with its edge portion in the said recess. In a further embodiment the metal foil disc is coated on either side with a thermoplastic material, this coating layer in the edge zone of the metal foil disc being pressed out a little with the help of heat and pressure over the edge zone of the metal foil disc and induced to combine together by fusion, encapsulating at the same time the cut edge zone of the metal foil disc.
The invention will be described in the following with reference to accompanying drawings wherein